1. Field of the Invention
The present invention relates to spiral-link fabrics. More specifically, the present invention relates to spiral-link fabrics having “chain mail” intertwined coils for use on a papermaking machine and other industrial machines requiring fabrics/belts.
2. Description of the Related Art
While the use of this fabric will be described for the papermaking process, other industrial uses exist; such as belts/fabrics for DNT (double nip thickener) machines, sludge dewatering presses, bowling pin spotter belts, and in the production of certain nonwoven products by processes such as, but not limited to, hydroentangling (spunlace), spunbonding, or air laying.
During the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in a forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.
The newly formed cellulosic fibrous web proceeds from the forming section to a press section, which includes a series of press nips. The cellulosic fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two such press fabrics. In the press nips, the cellulosic fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the cellulosic fibers in the web to one another to turn the cellulosic fibrous web into a paper sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the paper sheet.
The paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The newly formed paper sheet is directed in a serpentine path sequentially around each in the series of drums by a dryer fabric, which holds the paper sheet closely against the surfaces of the drums. The heated drums reduce the water content of the paper sheet to a desirable level through evaporation.
It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speeds. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.
Fabrics in modern papermaking machines may have a width of from 5 to over 33 feet, a length of from 40 to over 400 feet and weigh from approximately 100 to over 3,000 pounds. These fabrics wear out and require replacement. Replacement of fabrics often involves taking the machine out of service, removing the worn fabric, setting up to install a fabric and installing the new fabric. Installation typically involves pulling the fabric body onto the machine and joining the ends of the fabric along a seam; thereby forming the fabric into an endless belt. It is important for the seam to exhibit operating characteristics similar to the rest of the fabric body in order to minimize periodic marking of the manufactured paper product.
A fabric may be formed completely of spiral coils (so called “spiral-link fabric”) as taught by Gauthier, U.S. Pat. No. 4,567,077; which is incorporated herein by reference. In such a fabric, spiral coils are connected to each other by at least one connecting pin, pintle or the like. In theory, the seam can therefore be at any location in the fabric body where a connecting pin may be removed.
Spiral-link fabrics offer a number of advantages over traditional fabrics. For example, the seam of a spiral-link fabric is geometrically similar to the rest of the fabric body, and is therefore less likely to mark the paper product being manufactured.
Unfortunately, the production of spiral-link fabrics is both labor-intensive and expensive. This is because spiral-link fabrics are constructed of many small spiral elements that must be coiled and assembled. The multiple manufacturing steps of coiling, interdigitating, and interconnecting the spiral coils make this process costly. Because each coil is of a relatively narrow width, a great many connections are needed to form a complete fabric. Each spiral coil is connected to the next by inserting a pin, pintle or the like through the small channel formed by the interdigitated coils. The resulting large number of pintles make the fabric diagonally stiff. In addition, the shape of the coil loops results in such close spacing when interdigitated (i.e. almost touching) that the pintles are almost entirely covered.
As a result of this diagonal stiffness and the ‘touching’ of adjacent linked coils at each pin, conventional spiral-link fabrics are extremely stable.
However, this stiffness can be detrimental if, for example, any of the support rolls or dryer cans in a dryer section are not all parallel to one another. This lack of diagonal ‘give’ can then cause the spiral-link fabric to edge-up and/or to guide poorly, eventually damaging the edges of the fabric as it contacts guards, frames, etc. . . . and eventually leading to premature replacement.
FIG. 5 is a diagram of a conventional interconnection between a right-turn spiral coil 501 and a left-turn spiral coil 502 for a prior art spiral-link 25 fabric. A pintle 503 is inserted between the interdigitated loops of the right and left turn spiral coils. Note the close spacing of the interdigitated loops which effectively covers the pintle. For clarity, the foreground portions of the coils are shown as solid lines while the background portions of the loops are shown as dashed lines.
The present invention overcomes these shortcomings by providing a spiral-link fabric which is more flexible, especially across the diagonal, and has improved spacing between the interdigitated coils (especially over the pintles).